The present invention broadly relates to image processing and deals more particularly with a system for processing image data from sparsely excited, very large imaging arrays.
New applications for imaging arrays require very large arrays of image detectors for detecting and locating the onset of a radiative event. For example, a satellite-based sensor can be used to stare at a particular region on the earth to detect extremely small radiative events, such as missile or spacecraft launchings or nuclear tests. In order to obtain the resolution necessary to detect these relatively small radiative events, very large photodetector arrays are required. For example, arrays of 10,000.times.10,000 picture elements (pixels) may be required to detect the radiative events in the application mentioned above. In order to sample an array of this size, for example, 10 times per second, an overall sampling rate of 10.sup.9 Hz is required. This, of course, creates extreme demands on the subsequent imaging processing.
In the past, the analog signals produced by the photodetectors in the array were converted directly to digital signals by A-to-D converters, and this digital data was subsequently processed using digital techniques. In order to quickly locate a sparsely excited area of interest in the array, the digital data was processed in a serial fashion to develop pointers which would assist the processor in determining the precise location of the excited pixels of interest. However, the time required for digitally processing the "pointers" was so great that little advantage could be obtained compared to a conventional approach of determining the area of excited pixels by processing the signals using selected algorithms. Thus, it would be desirable to process the pixel data information in a manner which would yield the pointers more quickly and thereby speed up the determination of the precise location of the exciting event in the image array.